An agnomen (Latin: [aŋˈnoːmɛn]; pl.: agnomina), in the Roman naming convention, was a nickname, just as the cognomen had been initially. However, the cognomina eventually became family names, and so agnomina were needed to distinguish between similarly-named persons. However, as the agnomen was an additional and optional component in a Roman name, not all Romans had an agnomen.
Pseudo-Probus uses the hero of the Punic Wars, Publius Cornelius Scipio Africanus, as an example:
Quintus Caecilius Metellus Pius (c. 128 – 63 BC) was a general and statesman of the Roman Republic. His father Metellus Numidicus was banished from Rome through the machinations of Gaius Marius. He, because of his constant and unbending attempts to have his father officially recalled from exile, was given the agnomen (nickname) Pius.
During the civil wars between 88 and 80 BC, Pius sided with Lucius Cornelius Sulla. He successfully commanded Sulla's forces in the northern theatre (northern Italy and Cisalpine Gaul). In 81 BC he became pontifex maximus, then consul the following year alongside Sulla. As proconsul Pius fought against Sertorius (a former supporter of Marius) on the Iberian peninsula; in the so-called Sertorian War. He served alongside Pompey slowly grinding down the rebels from 79 to 72/71 BC. For his victories during the Sertorian War he was granted a triumph.
Quintus Caecilius Metellus Macedonicus (c. 188 BC – 116 BC/115 BC) was a statesman and general of the Roman Republic during the second century BC. He was praetor in 148 BC, consul in 143 BC, the Proconsul of Hispania Citerior in 142 BC and censor in 131 BC. He got his agnomen, Macedonicus, for his victory over the Macedonians in the Fourth Macedonian War.
Quintus Fabius Maximus Verrucosus (/ˈfeɪbiəs/), surnamed Cunctator (c. 280 – 203 BC), was a Roman statesman and general of the third century BC. He was consul five times (233, 228, 215, 214, and 209 BC) and was appointed dictator in 221 and 217 BC. He was censor in 230 BC. His agnomen, Cunctator, usually translated as "the delayer", refers to the strategy that he employed against Hannibal's forces during the Second Punic War. Facing an outstanding commander with superior numbers, he pursued a then-novel strategy of targeting the enemy's supply lines, and accepting only smaller engagements on favourable ground, rather than risking his entire army on direct confrontation with Hannibal himself. As a result, he is regarded as the originator of many tactics used in guerrilla warfare.
Quintus Caecilius Metellus Numidicus (c. 155 BC – c. 91 BC) was an ancient Roman statesman and general. He was a leader of the Optimates, the conservative faction of the Roman Senate. He was a bitter political opponent of Gaius Marius. He was consul in 109 BC; in that capacity he commanded the Roman forces in Africa during the Jugurthine War. In 107 BC, he was displaced from his command by Marius. On his return he was granted a triumph and the agnomen Numidicus. He later became a censor, entering into exile in opposition to Marius. Metellus Numidicus enjoyed a reputation for integrity in an era when Roman politics was increasingly corrupt.